1. Field of the Invention
This invention relates generally to the field of perpendicular magnetic recording or write heads and more particularly, to write heads having laminated side shields with increased permeability for improved performance.
2. Description of the Prior Art
As the recording density of magnetic hard drives (or disk drives) increases, a physical limitation is experienced using longitudinal recording systems partly due to thermal relaxation known as super-paramagnetism. That is, the density requirements for meeting today's storage needs are simply not attainable with longitudinal recording systems. To provide further insight into this problem, it is anticipated that longitudinal recording systems will lose popularity as storage capacities in excess of about 150 Gigabytes-per-square-inches become a requirement. These and other factors have lead to the development and expected launch of perpendicular recording heads or write heads. Perpendicular recording is promising in pushing the recording density beyond the limit of longitudinal recording.
Accordingly, perpendicular recording potentially can support much higher linear density than longitudinal recording due to lower demagnetizing fields in recorded bits, which diminish when linear density increases.
A magnetic recording head for perpendicular writing generally includes two portions, a write head portion or head for writing or programming magnetically-encoded information on a magnetic media or disk and a reader portion for reading or retrieving the stored information from the media.
The write head or recording head of the magnetic head or disk drive for perpendicular recording typically includes a main pole and a return pole which are magnetically separated from each other at an air bearing surface (ABS) of the writer by a nonmagnetic gap layer, and which are magnetically connected to each other at a region distal from the ABS at a back gap closure (yoke). This structure is referred to as a single-pole write head because while a main pole and return pole are referred thereto, the return pole is not physically a pole, rather, it serves to close the loop with the main pole and the soft under layer for magnetic flux circuit.
Positioned at least partially between the main and return poles are one or more layers of conductive coils encapsulated by insulation layers. The ABS is the surface of the magnetic head immediately adjacent to the recording medium.
To write data to the magnetic medium, an electrical current is caused to flow through the conductive coil, thereby inducing a magnetic field through the write head yoke, fringing across the write head gap at the media. By reversing the polarity of the current through the coil, the polarity of the data written to the magnetic media is also reversed.
The main and return poles are generally made of a soft magnetic material. Both of them generate magnetic field in the media during recording when the write current is applied to the coil.
In perpendicular recording heads, writing and erasing of information is performed by a single-pole write head. That is, the return pole is, in essence, a misnomer because it does not actually serve as a pole. The single-pole or the main pole is composed of high moment magnetic materials, the most common example being cobalt-iron (CoFe) alloys.
FIG. 1 shows a portion of a prior art return pole 10 included within a perpendicular write head and at 12, there is shown a coil wrapped around the yoke to generate magnetic flux upon the presence of an appropriate level of current to the write head. And upon the occurrence of the latter, programming or writing occurs on the medium 16 where as each of the bit locations of the medium 16 experience electromagnetic field at the tip 14, a bit is programmed. Bit locations 18 and 20 are programmed in opposite polarity to each other. The goal is to program each bit location without any adverse affects on adjacent bit locations. For example, ideally, when the bit location 18 is being programmed, no flux is influencing adjacent bit locations thereto, such as the bit location 20. In prior art systems, one of the problems is undesirable programming or affect of adjacent bit locations during the programming of a given bit location.
Thus, the need arises to reduce the field affecting adjacent bits by increasing the permeability of the regions of the shields that surround the main pole. In other words, it is desirable to reduce Adjacent Track Interference (ATI).
FIG. 2 shows a top view of a characteristic domain structure of a piece of magnetic material used in a perpendicular write head. The domains 26-32 are shown as arrows in a manner forming a closed magnetic circuit as materials having magnetic characteristics tend to do. The domain structure is excited or energized at 24. The magnetization of the domains that are shown to be perpendicular to the direction of the energizing (the direction of the magnetic field) at 24 are typically easier to rotate and thus conduct magnetic flux than the domains that are shown to be in parallel to the direction of energizing at 24. Thus, if the magnetization of the domains is perpendicular to the direction of flux, the material is more permeable than when the domains are parallel to the direction of flux.
FIG. 3 shows an ABS view of a portion of a prior art write head having a trailing shield 34, side shields 40, a top pole 36 and a bottom return pole 38. At this point, it should be noted that while not shown, the main pole is generally shaped in a manner causing a tip or an extension thereof that is narrower than the remaining portion thereof to form a top pole, such as the top pole 36. The side shields 40 act to shield the top pole so as to reduce adverse affects on adjacent tracks during the writing of magnetic transitions (data) at a location on a given track. FIG. 4 shows a top down view of the domain structures associated with the side shield 40 of FIG. 3. When energized at 42, the problem becomes the difficulty associated with moving the domains that are in a direction parallel to the direction of the flux or energizing.
Thus, the need arises for a write head to include a side shield that is laminated to form a flux closure in the direction of its cross section and having higher permeability thereby reducing over writing of adjacent tracks of a disk and increasing performance.